MEMS devices often include one or more mechanically movable elements supported in spaced position above circuitry or other components of an underlying substrate. An example such device is a digital micromirror device (DMD) device which has movable mirror elements supported in spaced position above respective mirror positioning circuit elements formed on an underlying substrate. Another example is a pressure sensor device which has a movable membrane supported in spaced position above membrane displacement detection circuitry. Another example is a switching device such as shown in U.S. Pat. No. 7,317,232 B2.
The fabrication of such devices typically involves the formation of a layer of photoresist or other sacrificial material as a spacer layer over the substrate and formation of the movable element by one or more layers of metal or other material deposited over the spacer layer. Following formation of the movable element, the spacer layer is removed to leave the gap between the movable element and the substrate. In many such devices, the spacer layer is patterned with vias or similar openings prior to deposit of the movable element layers to enable formation of the support structure for the movable element prior to removal of the spacer layer and at the same time as the movable portion is formed. Examples of such fabrication are given in U.S. Pat. No. 6,960,305 B2, U.S. Pat. No. 7,317,232 B2 and U.S. Pat. No. 7,576,902 B2, the entireties of all of which are incorporated by reference herein.
When constructing MEMS device elements that are spaced by a gap from other parts of the MEMS device structure using the described techniques, control of the spaced element formation is typically limited to variations in the coating thickness of the sacrificial material layer level (vertically) and the ability to selectively etch different materials composing the vertical stack. This may not be overly restrictive for the formation of planar features, but may present challenges for the formation of corrugated or other non-planar features.
Single- or bi-axis stiffening or softening may be useful for thin film spaced MEMS device elements.
FIG. 1 illustrates examples of thin film non-planar cantilever structures having oppositely directed corrugations as well as a simple planar cantilever structure shown for comparison purposes. In the leftmost member, the corrugations run parallel to the line of attachment with the supporting structure so act to soften the cantilever and encourage vibrational flexing. In the center member, on the other hand, the corrugations run perpendicular to the line of attachment so act to stiffen the cantilever and resist vibrational flexing.
FIGS. 2A and 2B illustrate two approaches for providing two dimensional stiffness using bi-directional corrugations. Lines in the figure indicate topographically lower feature elevations. The member shown in FIG. 2A uses a modular approach with alternating regions of parallel and perpendicular corrugations. The member shown in FIG. 2B uses a more localized structure with defined points of criss-crossed parallel and perpendicular corrugation intersections.
Non-planar features may also be useful to impart anti-stiction characteristics to the movable elements. Bumps and similar features known for this purpose are, however, significantly larger than the non-planar features addressed herein.